Shell and tube heat exchanger

ABSTRACT

A heat exchanger is provided that includes a shell defining a first fluid space and one or more tubes within the first fluid space having interiors fluidly isolated therefrom. The tubes define a second fluid space and are configured to permit thermal energy transfer between the first fluid space and the second fluid space. One or more heat pipes are disposed within one of the first fluid space and the second fluid space and are configured to transfer thermal energy within the respective fluid space.

BACKGROUND OF THE INVENTION

The embodiments herein generally relate to heat exchangers and moreparticularly to shell and tube heat exchangers.

Numerous heat exchangers have been devised for transferring heat storedin a first medium or fluid to a second medium or fluid. One example of aheat exchanger for high temperature/high pressure applications is ashell and tube heat exchanger. Several features are essential forefficient heat transfer in shell and tube type heat exchangers.

A large tube surface area is necessary for effective heat transfer,wherein the surface area increases with tube length and tube diameter.However, the advantage gained from a larger tube diameter is offset by adecreased thermal energy exchange which results from the medium insideof the large tubes tending to flow through the middle area of the tubewhere thermal energy transfer is lowest rather than adjacent theperipheral tube wall where thermal energy exchange is greatest. Further,a long tube length poses a problem with longitudinal expansion. When ahigh temperature shell fluid is employed, the tube temperature increasesresulting in thermal expansion of the tubes, which can lead to damageand/or leaks between the mediums. Thus, there are size constraints thatimpact the efficiency of tube and shell heat exchangers, resulting insmaller heat exchangers.

Another factor affecting the thermal energy transfer between mediums isthe flow of the fluids in relation to each other. Optimum thermal energytransfer is achieved when the shell fluid and tube fluid are in acontraflow, or counter-flow, configuration allowing for small heatexchangers that are efficient. However, in extreme temperatureconditions, a counter-flow configuration may not be sufficient to warm acold fluid at the point where the cold fluid enters the heat exchanger.If the cold fluid is not warmed sufficiently, icing or other impacts onfluid flow may occur.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment, a heat exchanger is provided that includesa shell defining a first fluid space and one or more tubes within thefirst fluid space having interiors fluidly isolated therefrom. The tubesdefine a second fluid space and are configured to permit thermal energytransfer between the first fluid space and the second fluid space. Oneor more heat pipes are disposed within one of the first fluid space andthe second fluid space and are configured to transfer thermal energywithin the respective fluid space.

According to another embodiment, a method of transferring thermal energybetween two mediums is provided. The method includes providing a heatexchanger defining a first fluid space and a second fluid space that isfluidly isolated from the first fluid space, the heat exchangerconfigured to allow thermal energy transfer between the first fluidspace and the second fluid space, and providing one or more heat pipeswithin one of the first fluid space and the second fluid space, the heatpipes configured to transfer thermal energy within the respective firstfluid space or second fluid space.

Technical effects of embodiments of the invention include providing animproved heat exchanger that enables efficient thermal energy transferbetween mediums, or fluids, in a shell and tube heat exchanger that isconfigured for high pressure applications. Further, thermal energytransfer for a given heat exchanger size can be optimized in accordancewith embodiments disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional illustration of an exemplary shell and tubeheat exchanger;

FIG. 2A is a schematic view of a heat exchanger showing a parallel-flowconfiguration;

FIG. 2B is a relative temperature plot of the temperatures of themediums within the parallel-flow heat exchanger of FIG. 2A as they flowtherethrough;

FIG. 3A is a schematic view of a heat exchanger showing a counter-flowconfiguration;

FIG. 3B is a relative temperature plot of the temperatures of the fluidswithin the counter-flow heat exchanger of FIG. 3A as they flowtherethrough;

FIG. 4 is a cross-sectional illustration of a heat exchanger inaccordance with an exemplary embodiment of the invention;

FIG. 5 is a relative temperature plot of the temperatures of the fluidswithin the heat exchanger of FIG. 4 as they flow therethrough.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a cross-sectional illustration of an exemplaryshell and tube heat exchanger 100 is shown. The heat exchanger 100includes a shell 102 and one or more tubes 104 located within the shell102. Shell 102 defines a domed pressure vessel having a cylindrical body106, a domed first end 108, and a domed second end 110. Of course, thefirst and second domed ends 108, 110 could take on other shapes and/orgeometries.

The cylindrical body 106 defines a first fluid space, labeled asinterior shell space 112, located in the center of the shell 102 andbounded at a first end by a first tube sheet 114 and at a second end bya second tube sheet 116. The first end tube sheet 114 and the second endtube sheet 116 fluidly isolate the shell space 112 from a first endcavity 128 and a second end cavity 130. The first end cavity 128 and thesecond end cavity 130 are fluidly connected by the interior(s) of theone or more tubes 104. A second fluid space may be defined as the volumewithin the tubes 104, and may further include the first and second endcavities 128, 130. It shall be understood that in order for the firstand second end cavities 128, 130 to fluid connect to the tubes 104, atleast one tube 104 may pass completely through each tube sheet 114, 116.

A first medium 101, such as a fluid, flows through the shell space 112by entering the shell space 112 at a point 103 through first port 118and exiting the shell space 112 at a point 105 through second port 120.The first medium in the shell space 112 is in contact with the exteriorsurfaces of the tubes 104. This allows for thermal energy transferbetween a medium within the shell space 112 (first medium 101) and amedium within the tubes 104 (second medium 107), without mixing of thetwo mediums. The flow path of the first fluid within the shell space 112can be controlled or directed by the inclusion of one or more baffles122, 124. As shown in FIG. 1, the first medium enters the first port 118and flows downward, around the first baffle 122, upward and around thesecond baffle 124, and then downward and out the second port 120, asindicated by the arrows within the shell space 112. The first mediumgenerally flows from left to right in FIG. 1, and defines a first fluidpath.

A second medium 107 flows through the heat exchanger 100 along a secondfluid path. The second medium 107 enters the heat exchanger 100 at point109 through a third port 126 and enters the first end cavity 128. Thesecond medium 107 then flows through the tubes 104 and into the secondend cavity 130. The second medium 107 will then exit the heat exchanger100 at point 111 by way of a fourth port 132. Similar to the firstmedium 101, the second medium 107 also flows generally from left toright through heat exchanger 100 in FIG. 1.

As noted, the first tube sheet 114, the second tube sheet 116, and thetubes 104 fluidly isolate the first medium 101 and the second medium 107from each other to prevent mixing. This allows for the first medium 101and the second medium 107 to be of different compositions and, moreimportantly, of different temperatures. The tubes 104 are formed fromthermally conductive material(s) in order to transfer thermal energyfrom the first medium 101 to the second medium 107, or vice versa. Forexample, thermal energy from a relatively warm or hot medium can betransferred to a relatively cool or cold medium when passing through theheat exchanger 100.

In order to facilitate heating of a cold medium (or cooling of a hotmedium), the cold medium is passed through the heat exchanger 100 in oneof the shell space 112 and the tubes 104, such as shown in FIG. 1. Atthe same time a hot medium is passed through the heat exchanger 100 inthe other of the shell space 112 and the tubes 104. For example, thecold medium may be a fuel for an aircraft and the hot medium may be oilof an aircraft. Due to the low temperatures and other conditions offlight, the fuel may chill to temperatures that are sufficient to causeicing. The icing results from water that is in the fuel freezing andforming ice crystals that may clog lines through which the fuel flowsand either reduces the fuel flow or, in extreme cases, may prevent fuelflow entirely. To heat the cold fuel and prevent icing, the cold fuel ispassed through the tubes 104 and the hot medium, e.g., hot oil, ispassed through the shell space 112. The hot medium surrounds the tubes104 and transfers heat through the surfaces of the tubes 104, thusheating the fuel.

As shown in FIG. 1, the first fluid path and the second fluid path flowgenerally in the same direction, i.e., generally from left to right.This fluid flow configuration is a parallel-flow configuration (see FIG.2A). As an example, in parallel-flow heat exchangers, the two mediumsmay enter the heat exchanger 100 generally at the same end (118, 126)and flow in the same general direction, relatively parallel to oneanother (arrows of FIG. 1), to the other end (120, 132) of the heatexchanger 100. An advantage of a parallel-flow configuration is that thehottest point of the hot medium is adjacent to the coldest point of thecold medium. Accordingly, the two mediums start at the highesttemperature difference and approach the same temperature when they exitthe heat exchanger. Advantageously, in the case of aircraft fuel, aparallel-flow configuration can prevent icing at the point that the fuelis at it coldest by locating the hottest temperature oil in proximity tothe coldest fuel.

In an alternative configuration, one of the mediums flows from right toleft in FIG. 1, i.e., the fluids flow opposite to each other. This is anexample of a counter-flow, or contraflow, configuration (see FIG. 3A).In counter-flow heat exchangers the mediums enter the heat exchangerfrom opposite ends, for example, and flow in opposite directions. Thisresults in the temperature at the outlet/exit of each medium approachingthe temperature at the inlet/entry of the other medium. An advantage ofcounter-flow heat exchangers is that they can optimize the thermalenergy transfer efficiency between the mediums for given heat exchangersizes. Thus, a counter-flow configuration is preferred when size is aconstraint or factor.

FIGS. 2A, 2B, 3A, and 3B illustrate the differences betweenparallel-flow and counter-flow configurations.

Turning to FIG. 2A, a parallel-flow heat exchanger 200 is shown.Although schematically shown, elements of heat exchanger 200 aresubstantially similar to heat exchanger 100 of FIG. 1; thus likefeatures are preceded with a “2” rather than a “1.” In the parallel-flowheat exchanger 200, a first medium 201 is a relatively hot fluid thatenters on the left side of FIG. 2A at point 203, cools off as ittransfers thermal energy to the second medium 207 while passing throughthe shell space 212, and exits the heat exchanger 200 on the right sideat point 205. The medium fluid 207 is a relatively cold fluid thatenters on the left side of FIG. 2A at point 209, warms up as thermalenergy is transferred to it from the relatively hot first medium 201while passing through tubes 204, and exits the heat exchanger 200 on theright side at point 211. This configuration enables the hottest point ofthe hot fluid to be in thermal contact with the coldest point of thecold fluid. As the mediums 201, 207 pass through the heat exchanger 200,they will approach the same temperature, as shown in FIG. 2B.

A relative temperature gradient representative of the first and secondmediums 201, 207 passing through the parallel-flow heat exchanger 200 isshown in FIG. 2B. The solid line represents a relative temperature ofthe first medium 201 as it passes through the heat exchanger 200, frompoint 203 (inlet/entry) to point 205 (outlet/exit). The dashed linerepresents the temperature of the second medium 207 as it passes frompoint 209 (inlet/entry) to point 211 (outlet/exit). The arrows indicaterelative direction of flow of the two mediums 201, 207 through heatexchanger 200. As shown, the first medium 201 starts at a relativelyhigh temperature at point 203 and then decreases in temperature to point205 as thermal energy is transferred away from the first medium 201. Incontrast, as thermal energy is transferred to the second medium 207, thetemperature of the second medium 207 increases from point 209 to point211. The parallel fluid flow enables a high transfer rate of energy fromthe hot medium to the cold medium quickly, and thus prevents icing,e.g., the hot medium is provided at the coldest location in the heatexchanger to prevent icing in the cold medium. Specifically, when bothmediums enter the heat exchanger, the hottest temperature of the firstmedium 201 at point 203 is adjacent to the coldest temperature of thesecond medium 207 at point 209. This presents the highest temperaturegradient between the two mediums, and thus the best solution to countericing.

Turning now to FIG. 3A, a counter-flow heat exchanger 300 is shown.Although schematically shown, elements of heat exchanger 300 aresubstantially similar to heat exchanger 100 of FIG. 1; thus likefeatures are preceded with a “3” rather than a “1.” In the counter-flowheat exchanger 300, a first medium 301 is a relatively hot fluid thatenters on the left side of FIG. 3A at point 303, cools off as ittransfers thermal energy to the second medium 307 while passing throughthe shell space 312, and exits the heat exchanger 300 on the right sideat point 305. The second medium 307 is a relatively cold fluid thatenters on the right side of FIG. 3A at point 309, warms up as thermalenergy is transferred to it from the relatively hot first medium 301while passing through tubes 304, and exits the heat exchanger 300 on theleft side at point 311. This configuration enables the mediums tomaintain a relatively constant temperature gradient as they pass throughthe heat exchanger 300, as shown in FIG. 3B.

A relative temperature gradient representative of the first and secondmediums passing through the counter-flow heat exchanger 300 is shown inFIG. 3B. The solid line represents a relative temperature of the firstmedium 301 as it passes through the heat exchanger 300, from point 303(inlet/entry) to point 305 (outlet/exit). The dashed line represents thetemperature of the second medium 307 as it passes from point 309(inlet/entry) to point 311 (outlet/exit). The arrows indicate relativedirection of flow of the two mediums 301, 307 through heat exchanger300. As shown, the first medium 301 starts at a relatively hightemperature at point 303 and then decreases in temperature to point 305as thermal energy is transferred away from the first medium 301. Incontrast, the second medium 307 flows in the opposite direction, asindicated by the arrows, and is at the coldest temperature at point 309and the warmest temperature at point 311. The counter fluid flow enablesa consistent thermal energy transfer that is efficient and enables theheat exchanger 300 to be optimized for sizing.

Regardless of the type of heat exchanger, the principle of operation isto have two mediums of different temperatures brought into close contactbut prevent the mediums from mixing. This allows for cold mediums to bewarmed and warm mediums to be cooled without energy being added orremoved from the system; it is merely an exchange of thermal energybetween the mediums. Further, there is also a change in pressure in themediums, as the temperature changes, which transfers energy, e.g., apressure drop occurs as each fluid moves from the entrance of the heatexchanger to the exit of the heat exchanger, transferring energy. In theexample of heat exchangers employed in aircraft, size and weightconstraints apply, in additional to the requirement of providing avessel for high pressure mediums. Due to the size and weightconstraints, a counter-flow shell and tube heat exchanger provides thebest advantage, but due to icing problems during flight, parallel flowmay be preferred.

Turning now to FIG. 4, a heat exchanger 400 in accordance with anexemplary embodiment of the invention is shown. Heat exchanger 400includes similar features as heat exchanger 100 of FIG. 1; thus likefeatures are preceded with a “4” rather than a “1.” Similar to heatexchanger 100 of FIG. 1, heat exchanger 400 includes a shell and tubeassembly, with similar components as described above and is arranged asa parallel-flow configuration. The primary difference between heatexchanger 400 and the embodiments described above is the inclusion ofheat pipes 450, 452, which may be dimpled heat pipes. Heat pipes as usedherein refer to thermal-transfer devices that combine the principles ofboth thermal conductivity and phase transition to efficiently manage thetransfer of thermal energy between two solid interfaces. At a hotinterface of a heat pipe a liquid in contact with a thermally conductivesolid surface turns into a vapor by absorbing heat from that surface.The vapor then travels along the heat pipe to the cold interface andcondenses back into a liquid—releasing the latent thermal energy. Theliquid then returns to the hot interface through capillary action,centrifugal force, gravity, or other process, and the cycle repeats.

The addition of heat pipes 450, 452 allows for a parallel-flow heatexchanger to include the benefits of a counter-flow heat exchanger,i.e., optimization of thermal energy transfer efficiency, and thus thesize of the heat exchanger can be optimized with the benefits/advantagesof both parallel-flow and counter-flow heat exchanger configurations.The materials and mediums of the heat pipes are configured such that themediums of the heat exchanger will cause a phase transition of the heatpipe medium, thus enabling efficient intra-medium thermal transfer.

As shown in FIG. 4, heat pipes 450 are included within the tubes 404 ofthe heat exchanger 400. The heat pipes 450 allow for thermal energytransfer within the fluid that passes through the tubes 404. Similarly,heat pipes 452 are included within the shell space 412 and allow forthermal energy transfer within the fluid that passes through the shellspace 412. Accordingly, in heat exchanger 400, there are two types ofthermal energy transfer. First, thermal energy transfer occurs betweenthe first and second mediums through the tubes 404 without mixing of thefirst and second mediums, similar to that described above (inter-mediumthermal transfer). Second, thermal energy transfer occurs within thefirst medium and within the second medium because of the heat pipes 450,452 (intra-medium thermal transfer).

In operation, in the parallel-flow heat exchanger 400 of FIG. 4, thetemperature extremes of the two mediums occur at the entry point to theheat exchanger 400, which are adjacent. The first medium enters at thefirst port 418 at a high temperature (hot fluid), and the second mediumenters at the third port 426 at a low temperature (cold fluid). Thus,the hottest temperature of the first medium is adjacent to the coldesttemperature of the second medium, which prevents icing, as discussedabove with respect to a parallel-flow configuration. With the additionof the heat pipes 452, located in shell space 412, the high temperatureof the first medium within the shell space 412 is transferred toward theportions of the shell space 412 where the first medium is cooler.Similarly, in the tubes 404, the heat pipes 450 allow for the warmthermal conditions of the second medium located toward the second cavity430 to be carried back toward the first cavity 428, thus providingadditional heat to the cold second medium.

As shown in FIG. 5, a relative temperature plot representative of thetemperatures of the first and second mediums 401, 407 as they flowthrough heat exchanger 400 is shown. The entry points of first port 418and third port 426 are shown on the left side of the plot and indicatethe largest temperature difference between the two mediums. However,because the heat pipes 450 and 452 are included, the temperaturedifference between the first medium 401 and the second medium 407equalizes very quickly, and provides a relatively constant temperaturegradient between the first and second mediums 401, 407 throughout heatexchanger 400. This enables an optimized thermal energy transfer similarto a counter-flow configuration, but also includes the inlet temperatureadvantages of a parallel-flow configuration.

Advantageously, embodiments of the invention provide maximum thermalenergy transfer and maximum absolute pressure capability for a givenvolume. Furthermore, advantageously, icing within a fuel line, such ason an aircraft, can be efficiently prevented. Moreover, heat pipes addedto a shell and tube heat exchanger provide a uniform temperaturegradient and thermal energy transfer throughout the heat exchanger whilemaintaining the benefit of icing prevention and optimizing the heatexchanger size.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions, combination, sub-combination, or equivalentarrangements not heretofore described, but which are commensurate withthe spirit and scope of the invention. Additionally, while variousembodiments of the invention have been described, it is to be understoodthat aspects of the invention may include only some of the describedembodiments.

For example, although described herein as a particular shell and tubeheat exchanger in each of the embodiments, other types of shell and tubeheat exchangers may employ heat pipes without departing from the scopeof the invention. One such alternative configuration is a U-shaped shelland tube heat exchanger, with heat pipes located within the U-shapedtubes and within the shell space of the heat exchanger. Furthermore,variations of shell and tube heat exchangers may include any number oftubes, shapes, sizes, and/or configurations without departing from thescope of the invention. Moreover, although described above in FIG. 4with heat pipes located within both the tube space and the shell space,alternative embodiments may include heat pipes in only one of the tubespace and the shell space. Further, although shown as having a heat pipein each tube, this is merely an example, and any number of heat pipesmay be used in each of the tube space and the shell space of the heatexchanger. The mediums discussed above are also not limiting, and othermediums beside fuels and oils may be employed, either as the hot mediumor as the cold medium, and the type or composition of the medium is notintended to be limiting. Moreover, different types of heat exchangersthat are not tube and shell may employ similar heat pipes or heattransfer devices without departing from the scope of the invention.

Accordingly, the invention is not to be seen as limited by the foregoingdescription, but is only limited by the scope of the appended claims.

What is claimed is:
 1. A heat exchanger comprising: a shell defining afirst fluid space; one or more tubes within the first fluid space havinginteriors fluidly isolated therefrom, the tubes defining a second fluidspace and configured to permit thermal energy transfer between the firstfluid space and the second fluid space; and one or more heat pipesdisposed within one of the first fluid space and the second fluid spaceand configured to transfer thermal energy within the respective fluidspace.
 2. The heat exchanger of claim 1, further comprising a firstmedium configured to flow through the first fluid space, and a secondmedium configured to flow through the second fluid space.
 3. The heatexchanger of claim 2, wherein the first medium is a relatively hot oiland the second medium is a relatively cold fuel.
 4. The heat exchangerof claim 2, wherein the first medium and the second medium flow ingenerally parallel directions through the respective fluid spaces. 5.The heat exchanger of claim 2, wherein the first medium and the secondmedium flow in generally opposite directions through the respectivefluid spaces.
 6. The heat exchanger of claim 1, wherein the one or moreheat pipes define at least one first heat pipe disposed within the firstfluid space, the heat exchanger further comprising at least one secondheat pipe disposed within the second fluid space.
 7. The heat exchangerof claim 1, configured to be installed on an aircraft.
 8. A method oftransferring thermal energy between two mediums, the method comprising:providing a heat exchanger defining a first fluid space and a secondfluid space that is fluidly isolated from the first fluid space, theheat exchanger configured to allow thermal energy transfer between thefirst fluid space and the second fluid space; and providing one or moreheat pipes within one of the first fluid space and the second fluidspace, the heat pipes configured to transfer thermal energy within therespective first fluid space or second fluid space.
 9. The method ofclaim 8, further comprising providing one or more additional heat pipeswithin the other of the first fluid space and the second fluid space,the one or more additional heat pipes configured to transfer thermalenergy within the respective first fluid space or second fluid space.10. The method of claim 8, wherein the first fluid space is defined by ashell and the second fluid space is defined by one or more tubes thatpass through the shell.
 11. The method of claim 8, further comprisingproviding a first medium within the first fluid space and a secondmedium within the second fluid space.
 12. The method of claim 11,wherein the first medium is a relatively hot oil and the second mediumis a relatively cold fuel.
 13. The method of claim 11, wherein the firstfluid and the second fluid flow in generally parallel directions throughthe respective fluid spaces.
 14. The method of claim 11, wherein thefirst fluid and the second fluid flow in generally opposite directionsthrough the respective fluid spaces.